The present invention relates to a disk brake suitably used to apply braking force to a vehicle, for example.
A generally known disk brake includes a caliper and a torque receiving member slidably supporting the caliper through pin members and allowing the caliper to move in the axial direction of a disk. A friction pad is provided between the caliper and the disk and pressed against the disk by the caliper. First and second shim plates are provided between the caliper and the back of the friction pad such that the shim plates are overlaid on one another. This type of disk brake is disclosed, for example, in Japanese Utility Model Application Public Disclosure (KOKAI) No. 2-426 (1990).
In the conventional disk brake of the type described above, the caliper extends over from one side to the other side of the disk to press the inner and outer friction pads against the disk. The caliper has an inner leg portion disposed on the inner side of the disk, a bridge portion extending from the inner leg portion to the outer side of the disk, and an outer claw portion provided at the distal end of the bridge portion to lie on the outer side of the disk.
The inner leg portion of the caliper is slidably mounted on a mounting member which is secured to a non-rotating portion of a vehicle and which serves as a torque receiving member. The caliper is supported by the mounting member so as to be movable in the axial direction of the disk. Friction pads are provided on both sides of the disk. One friction pad is disposed between the disk and the inner leg portion of the caliper. The other friction pad is disposed between the disk and the outer claw portion of the caliper.
When the brake is activated, a piston provided in the inner leg portion of the caliper is caused to slide toward the disk by an externally supplied hydraulic pressure, thereby pressing the inner friction pad against the disk. In addition, the whole caliper slides toward the inner side relative to the mounting member by receiving counterforce from the piston, causing the outer claw portion to press the outer friction pad against the disk. Thus, the disk is given braking force from both sides by the friction pads.
In this case, each friction pad is dragged by rotational force from the disk during the braking operation, and the circumferential displacement of the friction pad is received by the mounting member. According to the conventional technique, one or two shim plates are attached to the backing plate of each friction pad. In the case of the outer friction pad, for example, the one or two shim plates are clamped between the back of the friction pad and the outer claw portion of the caliper when the brake is activated, thereby preventing the generation of brake noise or an extraordinary sound during the braking operation. Moreover, the two shim plates are mounted in such a manner as to be overlaid on one another, thereby improving the durability and resistance to deterioration of the inner shim plate, coated with rubber, for example.
According to the above-described conventional technique, of the first and second shim plates attached to the outer friction pad, for example, at least one shim plate that is pressed by the outer claw portion of the caliper is integrally mounted on the back of the friction pad.
When the brake is activated, the outer claw portion of the caliper strongly presses the friction pad against the disk through the shim plates. Therefore, the frictional torque acting between the friction pad and the shim plates in the circumferential direction of the disk increases, and it becomes easy for rotational force of the disk to be transmitted to the outer claw portion of the caliper through the friction pad and the shim plates.
Because the caliper is merely supported at its inner leg portion by the mounting member, if the rotational force of the disk is transmitted to the outer claw portion, the outer claw portion side of the caliper is dragged in the rotational direction of the disk, causing the caliper to be flexurally deformed to tilt with respect to the mounting member. Consequently, the outer claw portion of the caliper, which should press the friction pad against the disk in parallel, may be slightly inclined.
Accordingly, the conventional technique suffers from the problem that the pressing force (surface pressure) of the outer claw portion for pressing the friction pad to apply the brakes becomes non-uniform, and this causes the outer friction pad to wear non-uniformly, resulting in a reduction of the lifetime of the friction pad. Even after the brakes have been released, a large dragging torque acts, and the caliper tilts and presses the pad. Consequently, the variation in the thickness in the circumferential direction of the braking surface of the disk increases, causing judder or other similar problems. Thus, the conventional disk brake is likely to have adverse effects on the drivability of the vehicle.
In the conventional technique, the shim plate coated with rubber or the like and the caliper are brought into direct contact with each other. Therefore, when the brake is activated, the frictional torque occurring between the caliper and the friction pad (shim plate) further increases, and it is more likely that the caliper will be tilted by rotational force transmitted from the disk to the outer claw portion.